In recent years, a still-picture digital signal compression technique, JPEG (Joint Photographic Experts Group) and a moving-image digital signal compression technique, MPEG (Moving Picture Experts Group) are known as global standard techniques.
In these compression techniques, an image signal is orthogonally transformed by using DCT (Discrete Cosine Transformation), and subjected to the Huffman coding. Among the frequency components after the orthogonal transformation, the information of high frequency components are reduced, and further, in the Huffman coding, among the information representing these frequencty components, a longer Huffman code is allocated to information with lower probability of occurrence, while a shorter Huffman code is allocated to information with higher probability of occurrence. In this manner, the amount of data of the original image signal can be reduced.
Further, a known method in a Huffman-code decoding apparatus is to store decoded values from respective Huffman codes in a decoded value memory in advance, then when a Huffman code to be decoded is inputted, interpret the code length corresponding to the Huffman code and the priority order of the Huffman code in a Huffman code group having the code length, then read an actual address value in the decoded value memory containing the Huffman-code decoded values from an address memory corresponding to the code length, and read a decoded value for the Huffman code from a predetermined position of the decoded value memory in accordance with the address value and the priority order.
However, in the conventional Huffman-code decoding method, as the actual address values in the above-described decoded value memory are stored in the address memories corresponding to the respective code lengths, the entire capacity of the address memory is large.